1. Field of the Invention
The present invention relates to an image stabilizing apparatus, disposed within an optical apparatus such as monocular, binoculars, and video camera, for preventing optical images from being observed in a blurred state due to the fluctuation in emission angle of luminous flux from an observation object with respect to the optical axis of the optical apparatus when the optical apparatus is vibrated.
2. Description of the Prior Art
When an optical apparatus aimed at optical observation, such as monocular and binoculars, is operated as being held with a hand, when the optical apparatus is used in an airplane, vehicle, or the like in particular, the vibration or rocking of the airplane, vehicle, or the like is transmitted to the optical apparatus, so that the emission angle of luminous flux from an observation object with respect to the optical axis fluctuates, whereby the optical image to be observed often deteriorates. Even if the vibration transmitted to such an optical apparatus has small amplitude, the angle of fluctuation with respect to the optical axis is enlarged since the field of view is narrow in the monocular, binoculars, and the like, and since the observation object is viewed under magnification therein. Therefore, even at the time of rocking with a relatively low angle fluctuating speed, the observation object may rapidly move within the field of view, and go out of sight when the angle of fluctuation is large, which is inconvenient. At the time of rocking with a relatively high angle fluctuating speed, on the other hand, the angle fluctuating speed of the image of observation object is observed as being increased by the power of optical apparatus even when the fluctuation angle is relatively small, whereby the image blurs and deteriorates, which is inconvenient.
Conventionally, various image stabilizing apparatus for preventing observation images from being deteriorated due to fluctuations in the emission angle of luminous flux with respect to the optical axis due to the vibration and rocking transmitted to optical apparatus have been proposed.
For example, Japanese Patent Publication No. 57-37852 discloses binoculars comprising therein anti-vibration means utilizing a rotary inertial member (gyro motor) in order to correct the blur of observation images in the binoculars.
Namely, according to this technique, an erect prism is disposed on the optical axis between an objective lens and an eyepiece of the binoculars and is secured onto gimbal suspension means having the rotary inertial member attached thereto, such that the erect prism is held in substantially the same posture even when the binoculars are vibrated due to camera shake or the like, so as to prevent the observation image of binoculars from blurring.
In such a conventional technique utilizing a rotary inertial member and gimbal suspension means, while images can be stabilized with a high accuracy, a high-speed rotary member is required for yielding a large inertial force within a small space, and a high precision is needed since the vibration generated by the rotary member itself has to be reduced. Such demands for smaller size, higher speed, and higher precision are problematic in that they impose inconveniences in terms of cost, life, time required for attaining a necessary inertial force after the power is turned on, and the like. If the effective diameter of objective lenses is made greater along with the increase in power or resolution of binoculars, then the erect prism becomes larger, whereby a large inertial force is required, which enhances the above-mentioned problems, and the power consumption increases along therewith.
Therefore, the assignee of the present application has proposed an image stabilizing apparatus (Japanese Unexamined Patent Publication No. 6-250100) in which an angular velocity sensor is mounted to gimbal suspension means in place of the above-mentioned rotary inertial member, and the pivoting of the gimbal suspension means is controlled according to the output value from the angular velocity sensor, so as to fix the posture of the erect prism with respect to the earth (inertial system). According to this apparatus, the erect prism held with the gimbal suspension means basically has an inertial force. In particular, its posture-keeping capability against vibrations with relatively large amplitude is high with respect to high-speed vibrations with a high vibration frequency. Therefore, the control power for the rotational position according to the angular velocity sensor can be kept small. In other image stabilizing apparatus which drive vari-angle prisms or lenses, however, active driving sections are needed, and it is necessary for the driving sections to be operated at a high speed in order to correct large amplitude in high-frequency vibrations, whereby correction in a wide angle range is difficult.
When binoculars and video cameras are used, panning and tilting are often carried out at a high speed. For example, fast pan/tilt operations are required when flying objects such as birds and airplanes are observed while being tracked.
Hence, if not only the angular velocity of gimbal suspension means but also its angular position is detected, and feedback control is carried out for image stabilization according to both of the detected values, then the optical system within the apparatus can smoothly track the observation object in its moving direction upon tilting/panning.
Here, if the gain of feedback loop based on the angular position is nonlinearly enhanced when the pivoting angle of gimbal suspension means becomes greater as disclosed in Japanese Utility Model Publication No. 7-5727, then the trackability upon panning/tilting can fully be enhanced.
It is preferred that the observation object can be observed in a tracking manner in the state free of camera shake upon panning/tilting as well. In the case where the gain of feedback loop based on angular position is nonlinearly enhanced as described in the above-mentioned publication, however, the gain is kept higher throughout panning/tilting, whereby anti-vibration performances would be sacrificed during this time. Also, there occurs a problem that a time lag (time difference between the time when a pan/tilt operation is started and the time when the gimbal suspension means arrives at an angular position where it recognizes the pan/tilt operation) occurs after the starting of pan/tilt operation until the gimbal suspension means begins moving.
In view of such circumstances, it is an object of the present invention to provide an image stabilizing apparatus which can observe the observation object in a tracking manner while securing anti-vibration performances, such as improvement in the response of gimbal suspension means, upon panning/tilting.
While the angular velocity of gimbal suspension means is detected by an angular velocity sensor such as piezoelectric vibrator gyro, a CR circuit 92 is connected to the output side of this angular velocity sensor 91 as shown in FIG. 15A, so as to cancel offset voltages and temperature drift voltages, whereby a detection signal centered at a predetermined reference voltage Vref is outputted to an amplifier.
If the CR circuit 92 is provided as such, then the CR circuit 92 functions as a high-pass filter, whereby it becomes difficult to detect vibrations in a low frequency region such as camera shake.
As the capacity C of the capacitor 93 or resistance R of the resistor R constituting the CR circuit 92 is made greater, the detectable vibration can extend to a lower frequency range. Since the time constant xcfx84(=CR) becomes greater in this case, the stabilizing time (xcex94t) from the starting of pivoting control (power ON) until when the output voltage is stabilized becomes longer as shown in FIG. 16A. The behavior of gimbal suspension means during this time is problematic in that, as shown in FIG. 16B, it travels to an end of its operating freedom so as to abut to a mechanical stopper and then returns to the midpoint of operating freedom as the output voltage approaches the reference voltage Vref, thereby being likely to lose sight of the observation object.
If the stabilizing time upon starting the pivoting control is shortened, then the gimbal suspension means can be restrained from behaving unstably. Generally considerable as a method of shortening the stabilizing time upon starting the pivoting control is one in which an analog switch 95 is disposed in parallel with the resistor 94 of the CR circuit 92 as shown in FIG. 15B such that the resistor is short-circuited by the analog switch 95 upon starting the pivoting control.
Since the angular velocity sensor 91 is disposed within a very narrow space in optical apparatus such as monocular and binoculars, it is quite difficult to secure a space for installing the analog switch 95 on a circuit board thereof, and further cut down the cost.
In view of such circumstances, it is another object of the present invention to provide an image stabilizing apparatus which can stabilize the behavior of gimbal suspension means upon starting the pivoting control while extending the detectable vibration to a lower frequency region.
In a first aspect, the present invention provides an image stabilizing apparatus mounted in an optical apparatus having a monocular or binocular optical system in which an erect prism is disposed between an objective lens and an eyepiece, whereas the objective lens and eyepiece of the optical system are secured within a case;
the image stabilizing apparatus comprising:
gimbal suspension means, adapted to pivotally attach the erect prism to the case, having two pivotal axes extending sidewise and vertical directions of the optical apparatus, respectively;
an actuator for pivoting the gimbal suspension means about the two pivotal axes;
two angular position detecting means for detecting respective angular positions of the gimbal suspension means about the two pivotal axes;
two angular velocity detecting means, secured to the gimbal suspension means, for detecting respective angular velocities of the gimbal suspension means about the two pivotal axes;
feedback control means for driving the actuator, according to an angular position and angular velocity detected by the angular position detecting means and angular velocity detecting means, so as to fix the erect prism with respect to an inertial system and controlling the pivoting of the gimbal suspension means; and
gain enhancing means for enhancing a gain of a feedback loop based on the angular position when the angular velocity is at a first set value or higher until the angular velocity becomes a second set value or lower.
In this configuration, the second set value may be identical to or different from the first set value. However, it is preferred that the second set value be a value smaller than the first set value by a certain extent.
Preferably, the above-mentioned configuration further comprises gain switching means for enhancing the gain of feedback loop based on the angular position upon manual switching.
In a second aspect, the present invention provides an image stabilizing apparatus mounted in an optical apparatus having a monocular or binocular optical system in which an erect prism is disposed between an objective lens and an eyepiece, whereas the objective lens and eyepiece of the optical system are secured within a case;
the image stabilizing apparatus comprising:
gimbal suspension means, adapted to pivotally attach the erect prism to the case, having two pivotal axes extending sidewise and vertical directions of the optical apparatus, respectively;
an actuator for pivoting the gimbal suspension means about the two pivotal axes;
two angular position detecting means for detecting respective angular positions of the gimbal suspension means about the two pivotal axes;
two angular velocity detecting means, secured to the gimbal suspension means, for detecting respective angular velocities of the gimbal suspension means about the two pivotal axes;
feedback control means for driving the actuator, according to an angular position and angular velocity detected by the angular position detecting means and angular velocity detecting means, so as to fix the erect prism with respect to an inertial system and controlling the pivoting of the gimbal suspension means; and
gain enhancing means for enhancing a gain of a feedback loop based on the angular position until a lapse of a predetermined time after starting the pivoting control of the gimbal suspension means.
Though not restricted in particular, the gain characteristic of feedback loop based on the angular position within the predetermined time is preferably set such that the gain is fixed at a higher value immediately after starting the pivoting control and then gradually decreases.
Preferably, the predetermined time is set to substantially the same value as the time required for an output voltage from the angular velocity detecting means to converge onto a reference voltage Vref after a power switch is turned ON.